The present invention relates to intraocular lenses, and more particularly to intraocular lenses which can be inserted through small incisions into the eye. It further relates to intraocular lenses whose refractive power can be altered while positioned in the eye.
Intraocular lenses have gained wide acceptance recently in the replacement of human crystalline lenses after a variety of cataract removal procedures. One current treatment of cataracts is to surgically remove them through ultrasonic emulsificiation, so that the light can once again reach the retina. When the natural lens is removed to eliminate the cataract it may be replaced by an artificial lens. The preferred method for restoring vision is an aphakic patient is to surgically implant a lens, a so-called intraocular lens, within the eye. Such a lens, however, need not and generally is not removed. Also, since the intraocular lens is positioned in approximately the same position as the natural lens, it provides vision correction without undue magnification of the image.
A problem associated with the proper implantation of intraocular lenses is the accurate determination of the precise refractive power required for them. Based on measurements of the prescriptive power of the patient's natural lens and measurement of the depth of the eye, a relatively accurate determination can be made of the proper refraction or power of the intraocular lens to be placed in the patient's eye. In most cases, the aphakic patient can have an intraocular lens implanted which provides good distance visual acuity even though spectacles may be required for reading since the intraocular lens cannot change its refraction or power like a natural lens. However, in some cases the intraocular lens may not provide good distance visual acuity. Since an intraocular lens cannot be readily removed and a new intraocular lens with a different power surgically implanted without unduly jeopardizing the patient's vision, the patient must rely on spectacles to provide good distance visual acuity.
A disadvantage of conventional rigid intraocular lenses is that implantation of the lens requires a relatively large, often six to nine millimeters, incision in the ocular tissue, and present methods of cataract removal by phacoemulsification require only a 3.5 mm incision which may be closed with a single suture. This long incision surgical procedure can lead to relatively high complication rates, such as increased risks of infection, retinal detachment, and lacerations of the ocular tissues, particularly with respect to the pupil. Small incision intraocular lenses do exist though and examples of them include soft foldable silicone lenses, foldable silicone optics with conventional non-foldable haptics, hydrogel lenses which are inserted into the eye in a dry miniature state and which then absorb ocular fluid to expand to their full size, and rigid materials with an optic divided into three sections wherein the outer two nontransparent sections slide under the central transparent one to compress the size of the optic. Each has its disadvantages though including stability problems. Thus, a need has arisen for an improved small incision intraocular lens, whose refractive power is adjustable after implantation.